For example, a dipole-type RFID (radio frequency identification) tag that is used in the UHF band is known as a wireless tag. The dipole-type RFID tag is attached to non-metal objects, such as cardboard or clothing. When attached to a metallic surface, the dipole-type RFID tag stops transmitting radio waves, the gain of an antenna drops, and the matching between the antenna and a chip collapses, making it impossible for the dipole-type RFID tag to communicate with a reader/writer (RW).
A loop antenna is known as one example of an antenna that can be attached to metal. A loop plane is installed so as to be perpendicular to a metallic plane. Therefore, mirror current flows on the opposite side of the metallic plane, meaning that the loop antenna has a larger loop than what the loop antenna actually has. Therefore, the loop antenna can communicate even when attached to the metallic plane. The loop antenna is equipped only with a wire forming the loop and a chip connected to the wire to operate.
What is known as a related technology is a RFID tag in which an antenna sheet is wound around a dielectric substrate with both ends of the antenna sheet being connected in a chip portion. However, the cost of producing the RFID tag is expensive. Since a chip terminal and the end of the antenna are connected, the connection point is fragile and could peel off. In particular, the RFID tag that can be attached to a metallic plane is for example used in an automobile assembly line and attached to bodies. In this case, a powerful force could be applied to the RFID.
The following RFID tag is also known: a chip is mounted on one antenna sheet wound on a dielectric substrate, and both ends of the antenna come closer to each other and thus are C-coupled (capacitively coupled). Thanks to the C-coupling (capacitive coupling), both ends of the antenna are coupled in a RFID frequency band (860 MHz to 960 MHz, for example). The distance of a gap of the C-coupled portion needs to be of the order of several dozen micrometers. However, in reality, it is difficult to maintain the distance of the gap due to the bending of the dielectric substrate and other factors. Moreover, the cost of producing the RFID tag is expensive.    [Patent Document 1] Japanese Laid-open Patent Publication No. 2007-272264    [Patent Document 2] Japanese Laid-open Patent Publication No. 2008-90813
However, as mentioned in the above example of the wireless tag, it is difficult to produce a wireless tag that is able to communicate even when attached to metal and has stable performance.